1. Bow Echoes
By Matthieu Desorcy

2. What is a Bow Echo? Bowing pattern on radar
Severe straight-line winds at the surface
Cause about 1/3 severe wind reports in US
Have a specific structure with
rear-inflow jet reaching the surface
Originate from various storm modes
Typically need >2,000J/kg CAPE
Move quickly and accelerate

3. Structure L Note: Strong rear inflow jet reaching the surface
Mid-level low pressure
Surface high pressure (by cold pool)
Most lift near leading edge of cold pool = strongest updrafts L H H
Cross section taken from case-study of June 10, 2003 bow echo during near NE/IA border during BAMEX (Bow Echo and Mesoscale Convective Vortex Experiment)

4. Initial Stages and Types
BE = classic bow echo
BEC = bow echo complex (bow echo with other storm type embedded, ie. supercell)
CBE = cell bow echo (small scale bow echo)
SLBE = squall line bow echo, also known as line echo wave pattern. Part of elongated linear convective system.
Klimowski et al. 2004

5. Types (cont.)
Klimowski et al. 2004

6. Kilmowski et al. Data and Summary
Used 273 scenarios between in US
More squall line bow echoes as you head further east
Thunderstorm mergers likely to play a role in BE development - consolidating cold pools, but need more data
Also suggests that when initial cell that merges with another, the speed and direction is maintained by BE
Average life span higher further south in the plains
CAPE and LLJ could be the reasoning for this – easier to get widespread high value CAPEs in the region and a strong low-level jet

7. Mesovortices
Play a role in the production of straight-line winds and even tornadoes in bow echo events
Straight-line winds enhanced on south side of mesovortex because horizontal pressure gradient
Most often observed near the apex of the bow
Depends on the low level wind shear and strength (temperature contrast) of cold pool
Few to tens of kilometres in size
Observed while rear inflow jets are strengthening
Causes still under research

8. Mesovortices (cont.) Note:
The location of the mesovortice, just north of the apex of the bow
The damaging part of the mesovortex (strongest straight-line winds) is on the south side as it wraps around the descending rear inflow jet
Nolan Atkins & St. Laurent 2009

9. Mesovortice Theories Theory 1:
Horizontal vorticity from downdraft gets tilted, stretched by updraft along gust front creating the vortice
Theory 2:
Along the apex of bow echo stronger updrafts are produced (by either stronger downdrafts prior, or rear inflow jet)
Horizontal vorticity just behind gust front is tilted by the stronger updraft, which produces a cyclonic vortice just north of apex and anticyclonic one south of apex
Anticyclonic one not observed as much

10. Mesovortice Theory 2
Nolan Atkins & St. Laurent 2009

11. Other Bow Echo Characteristics
Can have bookend vortices during mature stage – also caused by tilting of horizontal vorticity by updraft
Larger in scale than mesovortices
Bow echoes can become derechos if they have path >400km and meet wind criteria
Shelf clouds will typically be visible along gust front of bow echo

12. Bow Echo Summary Produce strong winds, sometimes tornadoes
Rear inflow jet creates the strong winds
Bow echoes transition from other types of storms, some cases include cold pool consolidation
Can acquire characteristics that enhance tornado threat and winds locally (mesovortices)

13. Questions?

14. References:
Atkins, N. T & St. Laurent, M. (2009). Bow Echo Mesovortices. Part I: Processes That Influence Their Damaging Potential. Monthly Weather Review, 137, doi: /2008MWR2649.1
Atkins, N.T & St. Laurent, M. (2009, May). Bow Echo Mesovortices. Part II: Their Genesis. Monthly Weather Review, 137, doi: /2008MWR2650.1
Davis, C et al. (2014, August). The Bow Echo and MCV Experiment. BAMS, doi: /BAMS
Klimowski, B. A et al. (2004, February). Radar Observations of the Early Evolution of Bow Echoes. Weather and Forecasting (AMS), 19,